F＃：区分的联合字段上的属性？

Question

I can do this:

type AttrAttribute () =
    inherit Attribute ()

type MyDU =
    | [<Attr>]A of bool
    | [<Attr>]B of int * string
    | [<Attr>]C of byte * char * int64

... but is there any way to do this?

type MyDU =
    | A of [<Attr>]bool
    | B of int * [<Attr>]string
    | C of [<Attr>]byte * char * [<Attr>]int64

Apparently, the case values are just fields (eg let v = B (13, "oops") in (Microsoft.FSharp.Reflection.FSharpValue.GetUnionFields (v, v.GetType ()) |> fst).GetFields () ), so I'm hoping this is doable, somehow.

Answer 1

This is quite contrived:

type A_ = { [<Attr>] Item1 : int }
type B_ = { [<Attr>] Item1 : int; [<Attr>] Item2 : string }

type MyDU =
    | A of A_
    | B of B_

And

let v = A({Item1 = 1})
let record = ((FSharpValue.GetUnionFields (v, v.GetType ()) |> fst).GetFields ()) |> Array.head 
let attrs = record.PropertyType.GetProperties() |> Array.collect(fun p -> p.GetCustomAttributes(false))